The team’s identification of iso-propanol in space was made possible through observations of a particular star-forming region in our galaxy where many molecules have already been detected. Sagittarius B2 is located close to the center of our galaxy and is the target of an extended investigation of its chemical composition with the Atacama Large Millimeter/submillimeter Array telescope in Chile. Microwave-wavelength emission from molecules floating around in Sgr B2 provides spectral patterns that can be recognized back on Earth, but these patterns can be weak and difficult to distinguish from each other. ALMA’s introduction 10 years ago has made it possible to go beyond what could be achieved with earlier, single-dish telescope technology.
So far, the team’s ALMA observations have led to the identification of three new organic molecules (iso-propyl cyanide, N-methylformamide, urea) since 2014. The ALMA project’s latest result is now the detection of propanol (C3H7OH).
“Our group began to investigate the chemical composition of Sgr B2 more than 15 years ago,” said Arnaud Belloche from the Max Planck Institute for Radio Astronomy, the lead author of the detection paper. “These observations were successful and led in particular to the first interstellar detection of several organic molecules, among many other results.”
Propanol is an alcohol and is the largest in this class of molecule to be detected in interstellar space. It exists in two forms (“isomers”), depending on which carbon atom the hydroxyl functional group is attached to: 1) normal propanol, with OH bound to a terminal carbon atom of the chain, and 2) iso-propanol, with the hydroxyl bound to the central carbon atom in the chain. Both isomers of propanol in Sgr B2 were identified in the team’s ALMA data set; the first interstellar detection of normal propanol was obtained shortly before the ALMA detection by a Spanish research team with single-dish radio telescopes in a molecular cloud not far from Sgr B2. The detection of iso-propanol toward Sgr B2, however, was only possible with ALMA.
This research is part of a long-standing effort to probe the chemical composition of sites in Sgr B2 where new stars are being formed and understand the chemical processes at work during star formation. The goal is to determine the chemical composition of the star-forming sites, and possibly identify new interstellar molecules. Many of these molecules are formed on the surfaces of microscopic dust grains, where they remain until dust temperatures are high enough to release them.